The present invention relates to a limiting amplifier, which comprises at least one amplifier stage between an amplifier input and an amplifier output, said amplifier stage including at least one amplifying component and load components, and which has an output signal limiting means limiting the maximum amplitude and the amplification of the output signal.
The invention is directed to such applications of the signal amplification art where it can occur that an incoming signal needing amplification has so great amplitude variations that the greatest amplitude values thereof fall outside the dynamic range of a conventional amplifier, i.e. the range within which the amplification is linear. As an example signal transmission via fiber-optic links can be mentioned, where the amplitude of the optical signals can vary considerably from link to link depending upon the distance between sender and transmitter. In order to be able to cope with this variation the receiver can include a symmetrical limiting amplifier.
The use of limiting amplifiers in connection with signal reception on fiber-optic links is described for example in two articles in the journal IEEE Journal of Solid-State Circuits, viz. in volume sc-21, No. 6, December, 1986, with the title "Integrated Circuits for a 200-Mbit/s Fiber-Optic Link", and in volume sc-22, No. 4, August 1987, with the title "Bipolar High-Gain Limiting Amplifier IC for Optical-Fiber Receivers Operating up to 4 Gbit/s."
Through U.S. Pat. No. 4,528,515 a high-frequency differential amplifier is known, in which an emitter-coupled pair of transistors each has its transistor input stage, of which the transconductance of the transistors can be varied by means of a variable current source. The aim is to vary the bandwidth and the damping factor of the differential amplifier without decreasing its amplification and dynamic range.
Through the Swedish laid-out specification 457 922 (corresponding to EP 88850158.2) a device for use in an active filter is known, which includes a differential amplifier stage with a differential input and a differential output.
The differential amplifier stage has two sets of components between a supply voltage and a current generator. The components of each set on the one hand include an amplifying component with a control electrode and a main conducting path between a first and a second current electrode, on the second hand a first group of series connected diode components arranged in a series circuit with the amplifying component between the first current electrode and the current generator, and on the third hand at least a second group of series connected diode components in series or in parallel with said series circuit. The control electrodes are connected in opposition to each terminal of the differential input so that difference between the potentials on the current electrodes increases with increasing voltage over the differential input. At the other current electrodes the amplifying components are connected in opposition to each terminal of the differential output so that the voltage over the differential output varies with the difference between the forward voltage drops over the two amplifying components.
The current generator is so arranged that it tends to keep the sum of the currents through the amplifying components constant.